Scope and Scale

This is a drum that I beat from time to time, but this time I'll make some annotated notes. Most published fantasy campaign settings are quite large. At least an entire continent, if not considerably moreso. Most of them "zoom in" on an area that's a bit smaller, though, and the peripheries serve as fringe places where there's less development and more room for GMs to do their own thing, or it's where unusual places are that are "quirkier" than normal. It's my contention that you don't need nearly as much space as you think that you do. I've pointed out many times before that Nentir Vale, for instance, the implied setting for 4e and big enough for multiple full campaigns of adventure, is about 150x100 miles, or about 15,000 square miles. My setting is bigger, but then again, it's meant to be many campaigns, often with different themes and tropes. I had three areas, all maybe about Nentir Vale sized (maybe; I deliberately didn't actually scale it because I want the scale to be malleable as needed—but at least Nentir Vale sized in terms of how much stuff that there is to interact with, regardless of actual scale. In other words, Nentir Vale sized in scope if not necessarily scale.) I've kind of started added a fourth.

But I'm a world-builder at heart. I enjoy doing it for its own sake. I think it's tons of fun just to do even if I don't use the built world for anything.

For most people looking to run a game, you simply don't need as much world building as you think that you do. And if you do want to build grander, larger worlds, here's a few things for comparison:

Size of North America (including all of the US besides island territories, all of Canada, all of Mexico and Central America: 9.4 million square miles

Size of the contiguous 48 states: 3.1 million square miles—and certainly large enough to encompass many, many campaigns.

Size of Europe: 3.9 million square miles; a bit larger than the lower 48, but much more culturally diverse. 

Size of Australia: 2.9 million square miles; about 75% of Europe, and a little smaller than the lower 48.

Size of Great Britain: 80,823 square miles. Considerably smaller, and yet the subject of a vast number of historical drama, historical fiction, and certainly sufficient for a campaign. Compared to my rough estimate of the size of Nentir Vale, it's still several times larger. The entire British Archipelago is 121,684 square miles; most of that made up by adding Ireland, of course, but also the Inner and Outer Hebrides, Channel Islands, Orkneys, Shetlands, etc.

Size of Nottinghamshire: 834 square miles. Setting of the entire "Robin Hood campaign", if Robin Hood were indeed a campaign. The Black Arrow by Robert Louis Stephenson takes place in an even smaller area, mostly—in and around Tunstall hamlet, although of course the actual geography isn't super detailed. 

As another point of reference, the old Dungeoncraft articles by Ray Winninger, published very late in the 2e lifecycle (I mean, literally the last few months of it) suggested a wilderness map that's roughly circular with a 60 mile radius. Because A = πr², that's an area of over 11,000 square miles. Roughly similar to Nentir Vale. A little smaller, but probably not enough to matter. (Plus my Nentir Vale area is a pretty rough estimate anyway.)

Anyway, like I said; I encourage you not to bite off more than you can chew, unless you just really, really enjoy chewing (like I do, mostly) or don't mind never actually finishing, most likely, your world-building. You probably need much less world-building to successfully play than you think.